The invention relates, in particular, to a fluid-tight conduit vibration decoupling device having a bellows-type corrugated connecting element which permits changes in axial length and angular displacements. Such a connecting element is, however, sensitive to mechanical stresses especially torsional stresses, so that these stresses need to be by-passed around the connecting element by means of a force transmitting means commonly comprising an articulated spring assembly. Conduit vibration decoupling devices can be subdivided, in dependence on the way in which their articulated spring assemblies are designed, into those where the elasticity is provided by a coil spring extending circumferentially of the centre line of the decoupling device or by a wire cable spring element, and those in which individual spring units are provided. Examples of decoupling devices of the first type are to be found in the following publications: DE-A-44 01 827, EP-A-0 432 436, EP-A-0 615 595, U.S. Pat. No. 3,369,829, EP-B-747 582. The invention is directed to a conduit vibration decoupling device of the second type as is known e.g. from U.S. Pat. No. 5 299 827. In the prior device three annular cable spring units are provided, these being arranged around the periphery of an adjacent conduit connecting member at circumferentially spaced locations and each being rigidly connected to the housing and the conduit connecting member independently of one another. A large amount of space is therefore required between the housing and the conduit connecting member for accommodating these cable spring units so that the known decoupling device has a large radial dimension and this thus runs counter to the trend in the automobile industry towards lightweight, compact decoupling devices. In addition, the sensitive, bellows-type connecting element is not protected or is only protected to a limited extent from torsional stress. Furthermore, a decoupling device of the second type is known from EP-B-0 816 738 which, in contrast to the previously described known device, has the advantage that it can be fabricated and assembled in an effective easy manner whilst, at the same time, being of compact size. In this prior device three linear leaf spring units are disposed around the periphery of an adjacent conduit connecting member, the ends of said units being supported on the housing with a certain amount of circumferential play i.e. in "floating" manner. Further each spring unit engages with clearance the adjacent conduit connecting member and extends therethrough like a secant passing through a circle. The not play-free coupling of the spring units to the housing and the conduit connecting member can lead to the development of irritating noises in use. Furthermore, due to the floating support of the spring units, a relative rotation, even though of limited extent, between the conduit connecting member and the housing cannot be avoided so that the sensitive, bellows-type connecting element will be subjected to a certain amount of torsional stress, which, although lower than was the case for the decoupling device in the aforementioned U.S. Pat. No. 5,299,827, nevertheless may result in a shortening of its useful working life.
An object of the invention is to provide an improved conduit vibration decoupling device. Another object of the invention is to provide a conduit vibration decoupling device having an articulated spring assembly which can easily be manufactured and assembled. Still another object of the invention is to provide a conduit vibration decoupling device in which the bellows-type corrugated connecting element has a greater degree of protection against torsional stress. A further object of the invention is to provide a conduit vibration decoupling device in which the development of noise on the part of the decoupling device can be reduced and a reduction in the dimensions of the decoupling( device realized.